1. Field of the Invention
The present invention relates to a ball bushed bearing screw bolt and nut, and more particularly, a ball bushed bearing screw bolt and nut having a bearing bush around a ball bearing nut so as to decrease the frictional rotating resistance between the ball bearing nut and the bearing bush.
2. Description of the Prior Art
A ball bushed bearing screw bolt and nut is a mechanism which can inversely convert rotating power inputted from a ball bushed bearing nut into an linear thrust force along the axial direction of the screw bolt and nut. Since the motion of a ball bushed bearing nut is a rotational motion with respect to the apparatus it belongs, it is a conventional method to provide a slanted ball bearing between the screw nut and the mechanism bolt so as to minimize the frictional resistance therebetween. It has an inherent advantage that the slanted ball bearing has ability to withstand an axial load so as to maintain the apparatus in a definite position, but it has an inherent disadvantage that its structure is complicate and bulky as well.
One of the well known improved designs is shown in FIG. 6, as shown in FIG. 6, a ball bearing nut 2 is screw combined with a screw bolt 1, and a plurality of rolling balls 3 are rolling therebetween. A bearing bush 5 is further contactually surrounding on the ball bearing nut 2. A plurality of screwed grooves 21 and 51 are formed transversely along respective surfaces of the ball bearing nut 2 and the bearing bush 5 facing each other with a plurality of bearing balls 4 interposing therebetween. So as to make the two elements ball bearing nut 2 and bearing bush 5 relatively rotate with a low friction. A flange 52 is formed at the left side (see FIG. 6) of the bearing bush 5 with several threaded holes 53 thereon for engaging the mechanism to a load. In addition, for evading the infringement of dust into the bearing grooves 21, 51, a dust ring 8 is provided at the end terminal of the bearing bush 5. Since the bearing balls 4 have to withstand considerably strong axial force so that the outer diameter at the outer side of the bearing groove 21 is much greater than its minimum outer diameter with the result that the bearing bush 5 is shifted away from the axis center of the screw bolt 1 when assembling the bearing balls 4, and then filling the bearing balls 4 into the bearing grooves 21 and 51 through the largest clearance therebetween. In this situation, the possible amount of fillable bearing balls 4 are, at the most, ⅔ of maximum amount. This causes lowering withstandable load that further brings about the necessity of enlarging the diameter of the rolling balls 4 for compensation. In addition, it is found that there are shortcomings inherent to such design, first of all, accuracy of dimension of the bearing grooves 21, 51 can not reach as perfect as to a degree of zero error, a certain deviation in dimension of the bearing balls 4 must be allowed for adjusting their preload, second, replacing the rolling balls for regulating preload is a tiresome and time wasting work, and third, assembling the bearing balls 4 which are under preload is also not easy.
Another improved design is shown in FIG. 7, wherein the bearing bush consists of a main bearing bush 6, a sub bearing bush 7, and a preloaded ring 9. Since the preloaded ring 9 is separable from the composition, the adjustment of preload can be carried out by grinding out thickness of preloaded ring 9 without varying dimension of the rolling balls. Even so, the disadvantages existing in the design shown in FIG. 6 still have not been eliminated. In some other designs, an attempt for improvement is made by trying to form the preloaded ring 9 into a combination of two semi-circular preloaded plates. When assembling, at first both preloaded plates are taken out, next, shifting the two bearing bushes 6, 7 toward the center so as to fill the bearing balls 4 into the bearing grooves fully, and finally inserting the two preloaded plates back into respective bearing bushes 6 and 7. If it is desired to make enough room for filling the rolling balls when the two bearing bushes are shifted to the center, the thickness of the preloaded ring 9 must be made considerably thick. To insert two thick preloaded plates into a clearance between two firmly coupled components is not easy. Besides, after having in service for certain time, the preload of ball bushed bearing screw bolt and nut will be lowered due to worn out of the bearing grooves, further, vibration, over load of the mechanism etc., all result in decomposition of the semi-circular preloaded plates which at the final stage, leads to breakdown of the ball bushed bearing screw bolt nut and nut.
The object of the present invention is for eliminating the disadvantages and inconvenience inherent to the conventional technique as mentioned above such as complicated and bulky structure, less rolling balls, difficult to assembly, and susceptible to decomposition of the semi-circular preloaded plates thereby improving quality and reliability of the product.
To achieve the above mentioned object, the ball bushed bearing screw bolt and nut of the present invention comprises a screw bolt, a ball bearing nut, a main bearing bush, a sub bearing bush, a preloaded ring, a plurality of rolling balls, and a plurality of bearing balls. The surface of the screw bolt is formed with screw threads. The ball bearing nut is coaxially screw combined with the screw bolt. A plurality of rolling balls are provided between the screw bolt and nut for aiding mutual rotation of the two elements. The bearing bush fitting around the nut is constituted by a main bearing bush, a sub bearing bush, and a preloaded ring. Bearing grooves are respectively formed at the outer surface of the ball bearing nut and the inner surfaces of the main bearing bush and the sub bearing bush in transverse direction, and a plurality of bearing balls are provided in each bearing groove for decreasing frictional resistance between the main and sub bearing bushes and the ball bearing nut. The main bearing bush has a flange, while the sub bearing bush has a corresponding fission so that the two bearing bushes can be stably combined together to facilitate assembly work. In order to evade dust infringement into those bearing grooves, a dust ring is installed at each end of the bearing bush. The preloaded ring can be divided into two semi-circular plates. When filling the bearing balls into the left grooves , at first removing the main bearing bush to the left, then filling the bearing balls into the bearing grooves of the nut, and finally returning the main bearing bush to its initial position. Filling of the bearing balls into the right grooves may be accomplished in just the same way as described above except the sub bearing bush is at first removed to the right. Since the two bearing bushes and the bearing balls are loosely coupled, both operations filling the bearing balls and removing the bearing bushes are easy.